In certain multitarget situations when traffic is being observed by a police Doppler radar in the same lane as the patrol car and in the opposite lane, it is useful to be able to limit the targets whose speeds are displayed to targets only in the same lane or only in the opposite lane. The same is true for stationary operation at the roadside. Further, it is useful to be able to use the radar to search for only the strongest target or both the strongest target and the fastest target or only the fastest target.
Police Doppler fast Fourier transform digital signal processing radars which can find the strongest target ha e been in public use for many years starting with the introduction of the STALKER™ handheld, digital Doppler digital signal processing (DSP) radar by Applied Concepts, Inc. of Plano, Tex. Police Doppler fast Fourier transform digital signal processing radars which can find the strongest target or the strongest target with simultaneous display of the fastest target have been in public use for many years starting with the introduction of the STALKER DUAL™ dash mounted Doppler police traffic surveillance by Applied Concepts, Inc. of Plano, Tex. The STALKER DUAL™ dash mounted Doppler police traffic surveillance radar is fully described in U.S. Pat. No. 5,691,724 which has an effective filing date of Feb. 10, 1995, the full contents of which are hereby incorporated by reference. Police Doppler fast Fourier transform digital signal processing radars which can find the strongest target or the fastest target in separate searches selected by the operator have been in public use for many years starting with the introduction of the EAGLE™ dash mounted, digital Doppler DSP series of radars by Kustom Signals, Inc. of Lenexa, Kans. The EAGLE™ dash mounted, digital Doppler DSP series of radars are partially described in U.S. Pat. No. 5,528,246, the contents of which are hereby incorporated by reference. There is a significant difference between the STALKER DUAL™ dash mounted Doppler police traffic surveillance radar and the EAGLE™ dash mounted, digital Doppler DSP series of radars, as described in U.S. Pat. No. 5,528,246 in that in the STALKER DUAL™ dash mounted Doppler police traffic surveillance radars, there is no separate search for the fastest target which can be selected by the operator and which ignores the strongest targets. The STALKER DUAL™ dash mounted Doppler police traffic surveillance radar always searches for the strongest target even when the operator selects fastest mode, and will not search for a fastest target until a valid strongest target has been found.
All of the FFTs done in the STALKER™ handheld, digital Doppler digital signal processing (DSP) radar and EAGLE™ dash mounted, digital Doppler DSP series of radars are non-complex FFTs, and none of these radars had direction sensing capability. An analog Doppler radar that has direction sensing capability is disclosed in U.S. Pat. No. 5,557,281, the contents of which are hereby incorporated by reference. That radar discloses a quadrature shifted two channel Doppler signal that is processed by a PLL to lock onto the frequency of one doppler signals in one channel. Another set of circuits determines direction by examining both channels and sends a signal to the PLL line of circuitry to tell it which direction the target it is locked on is travelling. It is unclear if this analog radar is operative in a multitarget environment where the strength of the various targets is varying rapidly since it is unclear which target the PLL will lock onto and which target will be sensed for direction. It is possible that the direction sensing circuitry will tell the PLL circuitry the direction of a different target than the target to which the PLL is locked thereby causing an error.
Therefore, a need has arisen for a digital FFT radar with direction sensing capability. Further, a need has arisen for such a radar that can find the strongest or fastest and strongest target or the fastest target alone.